Although Microsoft has yet to fix an update that sent some Windows Vista machines into endless reboots, it spelled out on Friday several workarounds users can apply to regain control of those PCs.

Last week's update -- actually a pair of prerequisite files that modify Vista's install components to prep the operating system for SP1 (Service Pack 1) -- caused some systems to reboot over and over, while others simply balked at booting. On Tuesday, Microsoft reacted to a flood of reports on its support forums by pulling the files from Windows Update until it could determine what went awry.

Although some users managed to stop the rebooting on their own or with help from others posting messages to a Microsoft support newsgroup, Microsoft was officially mum on a fix or workaround until Friday.

The KB949358 support document confirmed what users had been reporting for more than a week.

"When you try to install an update from Windows Update on a computer that is running Windows Vista, you may receive the following message: 'configuring updates stage 3 of 3. 0% complete'," it read. "After you receive this message, the computer reverts to the screen that displays the same message. Additionally, the update is not installed successfully, and the computer restarts."

The document also gave users three ways to stop the rebooting and take back control of their PCs. It suggested that they try them in this order:

* Start Windows Vista by using the Windows installation media, and then select the "Repair your computer" option;
* Start the computer in Safe Mode, and then use the Repair or System Restore feature;
* Rename the "Pending.xml" file, and then edit the registry.

Most, though not all, users who had tried these earlier -- other users suggested the trio on the newsgroup days before Microsoft put its stamp on the fixes -- had reported they'd reclaimed use of their PCs.

Some wags on the support newsgroup, meanwhile, have dubbed the snafu "Microsoft's St. Valentine's Day Vista Massacre," a nod to the day when reports first filled the forum. Many of them also complained of poor-quality advice from Microsoft's phone support representatives but said that they'd managed to recover their machines using one of the three fixes the company outlined Friday.

"I received this update on Feb. 14, and it killed Vista," wrote a user identified as D Clarke on Thursday. "I spent most of two days on the phone with a Microsoft guy from India named 'Steve.'"

Rather than wait for the Microsoft rep to call him back, however, Clarke tried the "Repair your computer" option, the first one outlined in the support document posted Friday.

While a patched update isn't yet available, Microsoft remained confident that the delay would not ruin its release plans for SP1. "This will not affect the SP1 release schedule," a company spokeswoman said Thursday. "We are on schedule to release Windows Vista SP1 to Windows Update and the download center in mid-March and to users using Automatic Update in mid-April."